Field of the Invention
The present invention relates to an aluminum alloy forged material suitably used for an automobile, and a method for manufacturing the same.
Description of the Related Art
There is a prior art invention regarding an aluminum alloy forged material for a chassis member of an automobile (an aluminum alloy forged material used for an automobile), such as that described in Japanese Patent No. 3766357. Disclosed in the patent literature is an aluminum alloy forged material including Mg: 0.6-1.8 mass %, Si: 0.8-1.8 mass %, Cu: 0.2-1.0 mass %, mass ratio of Si/Mg is 1 or more, further including one or more elements of Mn: 0.1-0.6 mass %, Cr: 0.1-0.2 mass % and Zr: 0.1-0.2 mass %, and the remainder being Al and inevitable impurities. The aluminum alloy forged material of the composition has a thickness of the thinnest portion of 30 mm or less, electrical conductivity measured at the surface of 41.0-42.5 IACS % after artificial age hardening treatment, and 0.2% proof stress of 350 MPa or more.
Although the 0.2% proof stress of the aluminum alloy forged material disclosed in Japanese Patent No. 3766357 is defined 350 MPa or more, the largest value is about 370 MPa as demonstrated in its Examples. Furthermore, regarding mechanical properties, its tensile strength is less than 400 MPa while the forged material has an excellent elongation.
In recent years, increasing requirements of further weight reduction have been raised for aluminum alloy forged materials for automobiles. To satisfy the requirements, high mechanical strength is essential for the aluminum alloy forged materials. It was difficult, however, for the invention disclosed in Japanese Patent No. 3766357 to realize the high strength to implement the tensile strength, 0.2% proof strength, and elongation at sufficiently high level.